A persistent problem to the operator of a tractor or other vehicle spreading liquid chemical fertilizer over a planted field is that he cannot simultaneously observe the pathway through the planted crop rows and also observe the spray issuing from each nozzle. The operator simply does not have eyes in the back of his head. It is not an uncommon problem for nozzles to clog and for nozzles to cease to spray fertilizer as desired. Since uniform distribution of fertilizer is a key to a profitable harvest, the operator must either move very slowly through the field so as to observe both the pathway through the crop rows and the spray from the nozzle or a second operator must be hired to simply observe nozzle operation. Even this will not necessarily avoid uneven distribution (with the attendant streaking). It is not really possible, in many cases, to observe when a nozzle has slowed the delivery of liquid fertilizer but has not altogether stopped spraying.
The prior art has contemplated apparatus for detecting the clogging of orifices used for spreading particulate (powdered) fertilizers. See for example U.S. Pat. No. 3,443,724. One drawback of this device is that only after the orifice has been clogged for sometime is it possible to detect that the orifice has been clogged. If all of the orifices slowly constrict, there will be no indication of clogging as there will be no relative change in the condition of the sensing devices. Relative downward movement of the rods will not take place. Apparatus for measuring liquid flow or liquid level not related to monitoring of spraying of liquid fertilizer is known. See, for example, U.S. Pat. Nos. 2,523,666; 3,389,603; and 3,446,986.
It is an advantage according to this invention to provide a system for detecting the clogging of the nozzles on a fertilizer spraying boom that requires almost no additional fasteners or brackets or plumbing associated with the boom. If the nozzles normally turn into threaded sockets in the boom, the nozzles are removed and replaced by a short pipe threaded at each end. The internally threaded inlet port of the sensing module according to this invention is then turned on to the exposed end of the short pipe and the nozzle is turned directly into the internally threaded outlet port of the sensing nozzle. No additional fasteners or brackets are required.
The flow sensing module according to this invention is easily disassembled for cleaning and for removal or replacement of sizing sleeves which make the sensing module adaptable for monitoring a wide number of spraying rates. In other words, by simple and easy replacement of sleeves in the sensing module the threshold flow below which a warning is effected may be adjusted.
While the flow sensing module according to this invention is easily cleaned, it is also designed so that no pockets of still or very slow moving fertilizer liquid are present to accumulate whatever might settle out of the fertilizer liquid thereby fouling the piston in the sensing unit.